Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.47   3.693%   $63.7401   $63.74   $63.75   $63.70  
  Purchase #2 $184.71   6.821%   $197.3091   $197.31   $197.30   $197.30  
  Purchase #3 $65.78   12.833%   $74.2215   $74.22   $74.20   $74.20  
  Purchase #4 $216.53   13.546%   $245.8612   $245.86   $245.85   $245.90  
  Purchase #5 $77.49   6.813%   $82.7694   $82.77   $82.75   $82.80  
  Purchase #6 $135.75   12.730%   $153.031   $153.03   $153.05   $153.00  
  Purchase #7 $239.36   3.750%   $248.336   $248.34   $248.35   $248.30  
  7 purchase totals = $981.09       $1,065.2683   $1,065.27   $1,065.25   $1,065.20